Snap action thermal limit switch



Oct. 26, 1948. H. ULANET SNAP ACTION 'THERMAL LIMIT SWITCH Filed Dc. 18. 1945 Patented Gct. 26, 1948 UNITI-:o STATES PATENT oFFlc 2,452,508 A SNAI ACTION THERMAL LIMIT SWITCH Herman manet, Newark, N. J.

Application December 18, 1945, Serial No. 635,810 (ci. zoo-139) 6 Claims. 1

This invention relates to improvements in electrical switches of the thermal limit type adapted to automatically open with a snap action when temperature of a device or at a location served thereby exceeds a desired predetermined limit.

This invention has for an object to provide a novel snap action thermal limit switch, which is easily convertible for optional operation as either a self-resetting switch or a manually resettable switch.

The invention has for a further object to provide a novel normally closed electrical switch adapted to be opened by a bi-metallic element which is responsive to temperature rise; the movable contact means of which comprises a ilat carrier springr which is fixed by its opposite ends to a support so as to be subjected to compression stress adapted to dispose the same in arcuate or bowed condition relative to the plane o f its support, but

neverthless so as to be responsive to a proper directionally applied pressure, substantially perpendicular thereto, whereby it may be sprung or snapped across a center line from down-bowed to up-bowed position, or vice versa, to bring the movable contact means in closed or open relation, as the case may be, to a relatively stationary contact means cooperative therewith; said bimetallic element being adapted, in operation, to deilect the carrier spring in direction to separate the movable and stationary contact means.

The invention has for another object to provide a novel relative arrangement of the circuit make and break elements of the switch together with means for adjusting the same in relation to the thermostatic bi-metallic element of the switch, whereby to be actuated by the latter in response to temperature of a selected predetermined degrec; the arrangement of said circuit make and break elements being such that adjusting movement thereof relative to the thermostatic bimetallic element cannot disturb the normal initial relation oi' said make and break elements one to the other.

Other objects of this invention, not at this time more particularly enumerated, will be understood from the following detailed description of the same.

Illustrative embodiments oi' this invention are shown in the accompanying drawings, in which:

Fig. 1 is a top plan view of a self-resetting form of the switch of this invention, the same being shown in circuit closing condition; Fig. 21s a longitudinal sectional view thereof, taken on line 2 2 in Fig. 1; Fig. 3 is a transverse sectional view thereof, taken on line 3 3 in Fig. 2; and Fig. 4 is f invention.

The switch structure, according to this invention, comprises a metallic, and therefore electrically conductive, supporting frame plate II having a butt portion I2 integral therewith. Said frame plate Il per se is of rigid or inflexible character, and, to assure such rigidity, is provided with means to stiffen the same against bending, such e. g. as stifiening flanges or ribs I3 disposed to project angularly from the plane thereof along its longitudinal margins. The transverse zone I4 intermediate the body of said frame plate I I and its butt portion I2 provides a flexibly resilient section adapted to form a hinge-like connection about which the frame plate may be swung up or down, for purposes to be subsequently set forth.

The tension of such hinge-like connection is such as to normally but yieldably up-swing the frameplate relative to the horizontal plane of the fixed butt portion I2.

The body of the frame plate I I is provided with an elongated opening I5 of suitable length and width extending between inner and outer end portions thereof. Aligned with and extending longitudinally over said opening I5 is a flat carrier spring I6 of a width somewhat less than the width of said opening l5. Said carrier spring vI6 is fixedly anchored at its respective oppositeend portions Il to the body of said frame plate II by suitable fastening means, such e. g. as rivets Il. In such fixed relation, said carrier spring is subjected to a compression stress which is adapted to arcuately form or bow the body thereof relative to the fiat plane of its fixed ends and that of the supporting frame plate II in one direction or the other. As thus bowed, the spring body is yieldably responsive to proper directionally applied pressure perpendicular thereto, whereby it may be sprung or snapped across a center line or plane from up-bowed to down-bowed position, or vice versa. Said carrier spring I6 is provided, centrally of its arcuate or bowed portion with a conaesasoe carried by the frame plate ll, and comprises aV metallic, and therefore electrically conductive, arm 2li having a butt portion 2l disposed to underlie and to be amxed to the frame plate il, but spaced and electrically insulated from the latter by en interposed block or body ci insulation material 22. Said butt portion 2i and insulation material 22 is ilxedly secured to the fe plate il by suitable fastening means, such e. g. as rivet means 28. Said rivet means 23 being electrically insulated from both the frame member il and the butt portion 2l and arm by an insulating sleeve 2d and external insulation elements da and 2G. Said rivet means 2t is also utilized to secure a wear plate 2l' in placerelative to the upper or outer side or face of the frame plate il; said wear plate 2l being adapted to receive the operative thrust o means provided for adjusting the circuit make and break elements ci the switch relative to the thermostatic loi-metallic element of the switch, as will presently appear. From its xed butt portion @l said conductive arm El@ extends forwardly in aligned but downwardly spaced relation to and beneath the frame plate li and carrier spring it. Said arm 2t is provided at its free end portion, with a contact element 28 disposed to project from its upper side toward the contact element i9 of the movable contact means and in the path oi movement of the latter.

The thermostatic member of the switch cornprises a bimetallic plate 2d having a butt portion 8@ which is disposed to underlie and to be afiixed to the butt portion l2 of the frame plate il, but spaced and electrically insulated from the latter by an interposed block or body of insulation material el. From its ilxed butt portion tt, said blmetallic plate 29 extends forwardly in aligned but spaced relation to and beneath the aforesaid movable and stationary contact means. The free end portion of said bi-metallic plate 29 extends beyond the free end of the arm t@ of the stationary contact means, so as to underlie a prtion of the bowed carrier spring le' of the movable contact means. Suitably amxed to the free end portion of said bl-metallic plate 29 is an upstanding, electrically non-conductive push-linger 32, which is directed toward the carrier spring I6 of the movable contact means. Asrelated to and disposed beneath the movable and stationary contact means, said bi-rnetallic plate 29 is positioned at the under or inner side of the switch, and so as to lie closely adjacent to the surface of the heated body I0, when the switch is mounted upon and xed to said body. Said bi-metallic plate-29 is' so characterized, that, when expanded by heat radiated from the body IB, it is upwardly tion in assembled relation, suitable fastening means is passed through the assembly. A preferable form of fastening means comprises one or more hollow rivets 3d, the same being insulated from electrical contact with the conductive elements of the switch by surrounding sleeves 8l of insulation material; a bottom block or body g of insulation material 8S being preferably ineluded contiguous to the butt portion il@ oi the deflected, thus causing its free end portion to. i

move toward the carrier spring I8 of the movable contact means.

Mounted `on the upper or outer side of the switch is the butt portion 3l of a bracket arm 8G, the latter being upwardly offset so as to overhang the frame plate Il. Said butt portion 33 ofA bi-metallic plate 2t. Said hollow rivets t@ provide passages through which may be passed fas tening screws S9, whereby to secure the butt or heel of the switch to the body l@ upon which it is desired to operatively mount said switch.

Threaded through the bracket arm 86 is an adjusting screw Gli, which may be utilized foradlustably moving the frame plate il, and the movable andstationary contact means carried thereby, toward and from the push-linger 82 of the lol-metallic plate 29, whereby to selectively predetermine the temperature at which movement of said loi-metallic plate, when expanded and flexed by heat radiated from the body l0, will be sumcient to carry the push-linger 82 into switch opening engagement with the carrier spring EG. By turning said adjusting screw le inwardly, the same thrusts downwardly on the wear plate 2l, thus swinging the frame plate il downwardly about the exible connection lil by which it is joined to its butt portion i2, thereby moving the contact elements closer to the push-dnger 32, so that the latter becomes operative at a relatively low degree of temperature. By turning said adjusting screw it outwardly, said frame plate and the contact elements carried thereby, is permitted to move farther away from the push-nger 82 of the bl-metallic plate, so that the latter becomes operative at a relatively higher degree of temperature. Owing to the fact that both the movable contact element, comprising the carrier spring it, and the stationary contact element, comprising the contact arm 2li, are both carried by the movable or swingable frame plate il, it will be obvious that adjusting movement of the latter, will not interfere with or disturb the normal initial set relation of the make and break contact elements one to the other. This is of decided advantage, and permits of very precise adjustment of the switch for response to a selected degree of operating temperature.

Means is provided for connecting the frame plate li and carrier spring l supported thereby to one side ci an electrical circuit to be controlled by the switch. Illustrative of one form of such means, as shown, the same may comprise an exteriorly projecting pole piece Si having a binding screw d2 operative to mechanically and elec trically connect thereto a circuit wire (not shown). Similarly, means is provided for connecting the stationary contact arm 2b to the other side of said electrical circuit, an illustrative form of which, as shown, may comprise an exterlorly projecting pole piece d3 extending from the butt portion 2l of said arm, and having a binding screw 4d operative to mechanically and electrically connect thereto a circuit wire (not shown).

Means is provided in connection witlr the frame plate il which is cooperative with the carrier spring i6 of the movable contact means of the switch, and which is subject to adjustment whereby said carrier spring may be optionally controlled or set relative tothe frame plate so as to be either self resetting or returning toY a nor mal switch closed position, or manually resettable to such position. The means for this purpose comprises adjustable check lugs 45 which project longitudinally from the frame plate I I at the ends of the opening l5 of the latter so as to respectively overlie end parts of the bowed section of the carrier spring I6. As shown in Figs:

2 and 4 more particularly, if it is desired that):y the carrier spring I6 be controlled or set whereby especially when the carrier spring is moved to up-bowed or switch open position, a counter stress operative to automatically urge the up-bowed mid-position of the carrier spring back to downbowed switch closed position, when up-bowing pressure of the bi-metallic plate 29 is relaxed. As shown in Fig. 5, i1' it is desired that the carrier spring I6 be controlled or set whereby to retain an up-bowed or switch open position to which it has been moved, said check lugs are turned or bent upwardly or away from and out of contact with the end portions of the bowed section of the carrier spring, whereby al1 restraint upon the up-bowing stresses upon the carrier spring, once it is moved to up-bowed position, are removed, so that said carrier spring will remain in up-bowed or switch open position until said up-bowing stresses are manually overcome. As also shown in Fig. 5, means may be provided for manually overcoming such up-bowing stresses, such e. g. as a manipulatable push-button 46 adapted to be supported in and by an extension 4l of the bracket arm 34, so as to engage the medial portion of the bowed section of said car'- rler spring I6. By reason of the provision of said check lugs 45, it will be obvious that the switch may be easily converted at will from a selfresetting type to a manually resettable type, or vice versa.

In the operation of the switch, the circuit controlled thereby is used to Venergize suitable electrical heating means (not shown) for heating the body IU. As the temperature of the heated body IU rises. heat radiated or conducted therefrom is transferred to the bi-metallic plate 29. Under the inuence of the applied heat, said bi-metallic plate is -deilected or warped, whereby to cause its free end portion to move toward the downbowed carrier spring I6, until, on attaining a desired temperature degree to which the switch is adjusted to respond, the push-finger 32 engages and pushes upwardly upon the carrier spring I6, whereby to up-bow the mid portion of the same with a rapid snap action, thus separating the contacts i9 and 28 and interrupting the controlled electrical circuit. If the carrier spring is controlled by the check lugs 45 so as to be self returning, said carrier spring will snap back to switch closing position, when, under temperature drop, the bi-metaliic plate 29 contracts to normal initial condition. This is due to the fact that the up-bowing of the mid-portion of the carrier spring, which extends inwardly of the engaging check lugs 45, is accompanied by downbowing of end portions of said carrier spring, which respectively extend outwardly of the engaging check lugs. Said down-bowed end por- [lli lli

tions exert a counter stressing eii'ect upon said up-bowed mid-portion of the carrier spring when Lip-thrusting pressure of the push-finger 32 is withdrawn, so that said mid-portion 0i the carrier spring will be snapped back to normal downbowcd switch closing condition. Under these circumstances the extremities of the check lugs 45 serve as fulcrums between the stressed up-bowed mid-portion of the carrier spring and the counter stressed down-bowed end portions of the latter. If the carrier spring is relieved from the restraint of the check `lugs 45, said carrier spring will remain in up-bowed switch opening position, until manually down-bowed to switch closing position. If desired an electrical resistance may be applied to and around the bi-metallic plate 28 for electrically heating the same, whereby the switch may be operated as an overload circuit breaker, relay or thermal timer.

I am aware that changes could be made in the above described thermal limit switch without departing from the scope of this invention as deilned in the here following claims. fore intended that all matter contained in the foregoing description or shown in the accompanying drawings shall be interpreted as illustrative and not in a limiting sense.

I claim:

1. In a snap action thermal limit switch having a stationary contact means and a movable contact spring, and a frame plate provided with an elongated opening bridged by said Contact spring, said contact spring being xed by its opposite ends to said frame plate under compression stress operative to bow its mid-portion, an adjustable means connected with said frame plate disposed to overhang an end portion of the frame plate opening, said adjustable means being adapted to be moved to optionally position the same out of engagement with the contact spring or so as to intersect the plane of a iixed end of said contact spring,r and thus to engage and pre-stress the contact spring toward the stationary contact means.

2. In a snap action thermal limit switch having a stationary contact means and a movable contact spring, and a frame plate provided with an elongated opening bridged by said contact spring, said contact spring being fixedby its opposite ends to said frame plate under compression stress operative to bow its mid-portion, bendable check lugs integral with the frame plate disposed to respectively extend over the respective end portions of the frame plate opening, said lugs being adapted to be optionally bent angularly to the plane of said .frame plate in one direction or the other, whereby to be selectively positioned out of engagement with the contact spring or so as to intersect the plane of the xed ends of said contact spring and thus to engage and pre-stress the contact spring toward the stationary contact means.

3. In a snap action thermal limit switch having a frame plate provided with an elongated opening, a movable contact spring bridging said vframe plate opening and fixed by its opposite ends to said frame plate so as to be subject to compression stress adapted to bow its mid-portion, a stationary Contact means subject to engagement by said movable contact sprin and a temperature sensitive element having a push linger directed toward said contact spring and operative upon deflection by heat to engage and bow said contact spring in direction to disengage said stationary contact means, an adjustable means connected with said frame plate disposed to It is thereattacca overhang an end portion of the frame plate opening, said means being adapted to be adiusted to optionally position the same out of engagement with the contact spring or so as to intersect the plane ofa ilxed' end of said contact spring and thus to engage and pre-stress the contact spring toward the stationary contact means.

4. VIn a snap action thermal limit switch having a frame plate provided with an elongated opening, a movable contact spring bridging said frame plate opening and xed by its opposite ends to/ said trame plate so as to 'be subject to compression stress adapted to bow its mid-portion, a stationary contact: means subject to' engagement by 'said movable Contact spring, and a temperature sensitive element havinga push finger di' rected toward said contact spring and operative upon deflection by heat to engage and bow said contact spring in directionV to disengage said stationary contact means, a plurality of adjustable means connected with said frame plate respectively disposed to overhang the respective end portions of the frame plate opening, said adjustable means being adapted to be moved to optionally position the same out of engagement with the contact spring or so as to intersect the plane q the fixed ends of said contact spring and thus tY gage and pre-stress the contact spring toward' `fe stationary contact means.

5. agsnap action thermal limit switch having a framegpiate provided with an elongated opening, a movableI contact spring bridging said frame plate opening and xed by its opposite endsto said frame plate so as to be subject to compression stress adapted to bow its mid-portion, a stationary contact means subject to engagement by said-fmovable contact spring, and a temperature sensitive element having a push nger directed toward said contact spring and operative upon deflection by heat to engage and bow said contact spring in direction to disengage said Astationary 'cont-,act means, a bendable check lug integral with the frame plate disposed to extend over an end portion of the frame plate opening, said lug being adapted to be optionally bent angularly ,to the plane of said frame plate in V one direetionlor the other, whereby to be selectively positioned out of engagement with the con tact spring or so as to intersect'the plane of the xed ends ofzsaid contact spring and thus to engage and pre-stress the Vcontact spring toward the'stationary contact means.

6. In a snap action thermal limit switch having a frame plate provided with an elongated opening, a movable contact spring bridging said frame plate opening and xed by its'oppo'site ends to said frame plate so as to be subject to compression stress adapted to bow its mid-portion, a stationary contact means subject to engagement by said movable contact spring, Vand a temperature sensitive element having a push finger directed toward said contact spring and operative upon deflection by heat to engage and bow said contact spring in direction to disengage said stationary contact means, bendable check lugs integral with the frame plate disposed to respectively extend over the respective end portions of the frame plate opening, said lugs being adapted `to be optionally bent angularly to the plane of said frame plate in one direction or the other, whereby to be selectively positioned out of engagement with the contact spring or so as to intersect the plane of the xed ends of said contact spring and thus to engage and ypre-stress the contact spring toward the stationary contact means.

REFERENQS CITED 

